In an IC card which the present inventors have studied, the reading and writing of data from and to memory are managed by the function of a CPU (Central Processing Unit) incorporated in the IC card, and a high security function is ensured in which a cipher processing is executed by the card itself. Further, its memory capacity is 30 to 100 times larger than that of a magnetic card. Thus, the IC card in question is expected to see considerable use as an information storage medium in various fields, including finance, distribution, medical care, traffic, transportation, and education. In a general IC card structure, a recess is formed in part of a plastic sheet, which is about the size of a name or business card, and a packaged semiconductor chip is embedded therein. As a top layer of the semiconductor chip, there is a surface protecting film formed of an insulating material so as to cover the whole of the main surface of the semiconductor chip. Wiring lines, such as bus lines and control lines arranged on the main surface of the semiconductor chip are covered with an overlying multi-layer interconnection.
A technique for improving the information security of a semiconductor device is described, for example, in Japanese Unexamined Patent Publication No. Hei 11 (1999)-145401, which technique involves the provision of a conductor layer serving as a shield layer that overlies and covers the semiconductor element so as to prevent access to the wiring lines thereof. However, the present inventors have found that the following problems are inherent in the IC card security technique described in this publication.
One problem with the above-described security technique is that, if the semiconductor device is operated after removing the whole of the shield layer with a chemical and if, in this state, a needle for analysis is brought into direct contact with a bus line or a signal line, it is possible to analyze information stored in the semiconductor device. In addition, although bus lines and signal lines are covered with the multi-layer interconnection, an uncovered gap will typically occur in an input port of a module or the like in relation to the layout of the power supply wiring. There may occur a case where information stored in the semiconductor device can be analyzed by the application of an analyzing needle through such a gap.
It is an object of the present invention to provide a technique for improving the security of information stored in a semiconductor device.
The above and other objects and novel features of the present invention will become apparent from the following description and the accompanying drawings.